Why aren't there any green mammals?

Question

Don't say sloths because they aren't

Answer 1

Mainly because we/they are hairy and most pigment fades in daylight and can't be replenished because the shaft is dead.

Mammals also evolved from mostly nocturnal animals, which benefited from the dark/drab coloring.

There are some mammals that have brightly colored faces and such, from blood flushing and skin patches from collagen ... but for the most part, we are a drab bunch.

Answer 2

No one knows for sure. Mammals are overwhelmingly earth-colored - mousy, you could say. A few sort-of-green mammals do exist: Tree sloths turn grayish-green when algae grows on their fur. Australia's ringtail opossums have bands of black and yellow on their hair that can look a grizzled olive drab. You could argue that a diatom-encrusted whale is green. But nonmammal tree frogs, praying mantises and parakeets are all luminous, unapologetic greens. Green vegetation fills the natural world, and many of its denizens use green as camouflage. Why not mammals?

The short answer is that mammals are hairy. Mammalian hair has only two kinds of pigment: one that produces black or brown hair and one that produces yellow or reddish-orange hair. Mixing those two pigments is never going to yield a bright, contestable green.

Mammalogist Maria Rutzmoser of Harvard's Museum of Comparative Zoology suggests a more complex explanation: that small mammals - the ones needing protective coloration the most - typically live on the ground, scurrying in leaf litter. "Dead leaves aren't green," she points out. "They're brown."

Finally, most predators of mammals are other mammals, and mammals usually have poor color vision; ergo, green wouldn't help.

Still, evolution has given us wonders ranging from the hawk's retina, to the mathematician's brain, to the lion's roar. Given enough time, natural selection could surely produce green fur.

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